Black screen television cathode-ray tube



Oct. 28, 1952 I w. COLTMAN BLACK SCREEN TELEVISION CATHODE-RAY TUBE Filed May 20, 1950 Glass Tube Face Lampblack Transparent Phosphor Layer INVENTOR John W. Coltman.

Y %ZM f ATTORNEY Patented Oct. 28, 1952 UN IT 'PATE'N T ""BIJACKSCREEN TELEVlSlON CATHODE-RAY TUBE a zJoli-m'w pjcoltman; Pittsburgh; Pa., assignor .to

-Westinghuses-Electric Corporation, East Pitts- .burgh,.-Pa al'corporation of Pennsylvania My: invention 'rlatestofluorescentiscreensand {in particular 'to*fluorescent "screens :for'. use with cathode ray tube apparatus.

-A cathode ray tube havingafiuorescent screen,

i which is characterized by providing a highcontrast, that -is a 'highfratio of brightnesses of the light anddark areas on the tubes'r'fluorescent s'creen whenyviewed "from a' 'position external to f the tube, *is highly desirable"; especially for use 1 in television=receivers.

"In accordance with"thefpriorart of'which' 'I am aware; ambient illumination, that is',-il1urnination striking the external side of the fluorescent screen from light sources'out'side 'the cathode ray *tnb, has a ten'dency to impair high-image con trast byincrea'sing the"apparen't brightness of --'-the darkareas." l-rna'ge contra's't 'is also' impaired by the' introduction of -'halation 'efiects due to "internal light reflections b'etweef-the"respective surfacesof the glass tube" f ace, "and by: diffused reflection and scattering :of' 'light rays in the =scr'een material"to illuminate*anarea surround- 'ing l the spot excitedby the electron beam; In an efiort to overcome the first objectionablecharcharacteristics has 'been to'placaa dark material in the glass of the tube faceitself;butthisapproach is also subject to considerable objections of a similar nature.

It is an object of my invntion to provide an improved *fluor'escent screen" -f0r cathode ray "tubes.

Itis another objectof rn-y invention'tolnrprove the contrast ratio of fluorescent screena It isanotherbb'j ectof' my invention-to? improve the contrast ratio of "the screen when said screen is ekposed -'to '"ambient illumination.

It is a'further objecto'f my invention to; sub-'9 -"stantially eliminate halatio'n" effect or light reflected within the tub'e'face.

- sun another object of' my invention is to9pj o- -vide a'dark 'face fluorescent-screen cathode 'ray tube which requirsno external light filtering" apparatus.

-An additional object ofm yinv ention is toplrovide fa better 'contrast ratiof-for"the fluorescent screen and at the sarne time'require noexternal light filters or light absorbent rnaterials betweerf' the fluorescent screen and the observers.

' still additional" objectxis I to fprovi'de an: impro'vedmethod for-making fluorescentscreens'for 1950, Serial No. 163,121

"'53; method :or manufacturing a (fluoresqentgscreen which; is -characterized; by ;1 a. desirable :contrast iratimunder. conditions of ambient. illumination.

Iii-accordance withxmy'invention a phQ Rhor 5 riayer: is placed on :the ginternalzsurface ;of .Ithe rcathode; rayitube: face-said phosphorrlayer? being in the :form .of a transparent thin glassy layer which is characterized by --a,..structuref:which does not substantially diffuse lightthat impinges l0 uponit. In' the following, thewordsftransparenti-rand glassy as applied to the phosphor layer hare fused .to describe the substantially nonedifiusing character of the" layer'with respect to .lightrays, is "although ithe'm'aterial 'of' the layerrmaylihave an organized crystalline structure in the chemical sense. A light absorbent coating: is subsequently placed on the inner-surface 'of:said phosphor layer away fromsaid tube face. 'Thisrcoating is of a thickness which does not impain'thes'op- 'er'ationIof the cathode'ray tube'electron beam toexcite the "fluorescent layer,"however,' this coat- ;ing is of such thickness that ambienfillumina- "tion irom light sources external-to the cathode "ray tube is substantially absorbed and znot reffle'cted back in a directiongenerallytowardthe externallight sources. The light absorbent c'oat- *ing can be madeof some material"such 'ascarbon deposited as lampblack, or". by I evaporating bertam" materials, such as "aluminum -or-antimony, for example, in a low pressure -atm'ospl'iere. Under these conditions black deposits rather than metallic appearing deposits, are 'obtained."The presence of the relatively thin light absorb'ent black layer on the backside of 'thetransparent phosphor layer givesthe appearance, when viewed irom the external, 'or front, side of the cathode "ray tube face, of a substantially blackscreen. vj The novel features that I cons'idejr characterj istic ofxmyi inventionareset forth with particu- 'larity ,inthe appended claims. Q'Thef-inve'ntion j itselfghowever, both 'as "to. its "organization'jand its'rnetho'd of operatiomtogether with additional objectsan'd advantages thereof willbest'beunderstood from the following description of" specific V embodiments when read in conjunctionwith-the accompanying drawing, in which:

Figure 1 of .the drawing illustrates ajcathode ray tube having a thin. lassylayerxof phosphor material deposited on the internal'side-off'the tube'face and ablacklight 'absorbentLcoating depositedon the internal surface of saidiphosphor layer.

Figure 2 of the drawing is a sectionalview of the cathoderay tube screen showing 'the' glass tube-face, the glassy-layer of phosphoran'dthe black coating placed on saidphosphor-layer.

The cathode ray tube 1-0 shown in '1 is presumed to have an electron gun for ge nerating ran electron b'eam; 'meansifor modulating the" ingeneous structure. ual crystals to reflect undesired light which falls on the screen. This is beneficial in the reduction of halation effects which are detrimental to tensity of the beam, deflection control means such as electrostatic deflection plates or magnetic deflection coils, a first accelerating anode, a second anode, and a tube face I2. On the internal surface of said tube face I2 is deposited a thin glassy layer of phosphor material to form a transparent fluorescent screen. On the internal surface of said phosphor layer is deposited a coating of light absorbent material.

The section of the tube face !2 shown in Fig. 2 includes a phosphor layer l4 deposited on the internal surface I6 of the tube face l2 which layer is in the form of a transparent glassy layer and is characterized by a substantially nondiffusing structure. A method for depositing -"si1'ch'a' phosphor layer M to form a fluorescent screen is described in United States Patent 1,954,691, to de Boer and Dippel. In accordance with the teachings of the latter patent, the fluorescent material is volatilized and precipitated in a vacuum to form a uniform layer It on the tube face 12 of such a thickness that it is substantially transparent to light rays.

. made from carbon in a simple manner by depositing it as lampblack from a source such as an acetylene flame. Another method of forming such a coating l8 would be the evaporation of certain light absorbent materials, such as aluminum or antimony, in a low pressure atmosphere, to form a black non-reflective coating. Such layers can readily be made thin enough to cause little loss of energy of the electrons passing through them at velocities corresponding to voltages commonly used in television cathode ray tubes, and still be substantially opaque to light.

In the section view of the cathode ray tube screen shown in Fig. 2, the phosphor layer It is shown contiguous to the tube face I2. And contiguous to the inner surface of such phosphor layer I4 is the thin coating l8 of non-reflecting light absorbent material.

The phosphor layer It which is precipitated and deposited on the inner tube face surface It isof a substantially non-diffusing and homo- Thus, there are no individpicture detail contrast. Halation occurs when light is reflected internally from the glass surface of the tube face 12, which in prior art devices illuminates the phosphor screen and surrounds the spot energized by the electron beam with a luminous halo. This is objectionable in that it causes those black areas of the screen image which are near bright areas to appear grayish in color. This is particularly objectionable in television receiver tubes.

My invention overcomes this halation effect and provides greater detail contrast in that both the non-diffusing fluorescent screen l4 and the contiguous black layer coating [8 on the back side of said screen are non-reflecting. Therefore, the internal reflections between the glass phor screen M as in prior art tubes.

v4 lar internal reflection between the surfaces of the tube face 12 due to a difference in refractive index of the tube face I2 and layer It will further not be objectionable in that this light will, in general, be trapped within the tube face l2 since the reflection angles are such that the major portion of the light cannot escape through the surfaces of the tube face I2.

Since the black coating I8 is behind the phosphor layer 14, there is relatively little absorption of desirable light from the fluorescent screen, so that high contrast ratios can be obtained. This is of particular importance respecting deep black portions of the image on the screen. Also, the non-cyystalline structure of the glassy phosphor layer It is-of importance in that there are no crystals to reflect light from sources external to the tube, and in this manner, the black areas of the image on the screen are not impaired by reflections of external light on the phosphor crystals themselves.

Although I have shown and described certain specific embodiments of'my invention, I am fully aware that many modifications thereof are possible. My invention, therefore, is not to be restricted except insofar as is necessitated by the prior art and by the spirit of the appended claims.

I claim as my invention:

1. In combination: a cathode ray tube having a tube face and electrodes for producing an electron beam; a fluorescent layer precipitated on the internal side of said tube face to form a transparent glassy layer thereon; and a coating of light absorbent material, of such thickness that the'operation of said electron beam is not impaired, adjacent said fluorescent layer on the opposite side of said fluorescent layer from said tube face.

having a tube face and electrodes for producing an electron beam, a layer of fluorescent material on the internal side of said tube face, and a layer of light absorbent material, respectingincident light rays, adjacent said fluorescent layer on the opposite side of said fluorescent layer from said tube face, said layer of light absorbent material being of such thickness that the operation of said electron beam to excite said fluorescent layer is not impaired.

3. A fluorescent screen on a television tube face, comprising the combination of a phosphor layer on saidtube face, said layer characterized by a substantially non-diffusing structure, and a coating of light absorbent lampblack on said phosphor layer.

4. A screen for a television tube having a tube face, comprising the combination of a fluorescent glassy layer on said tube face, and a coating of light absorbent material on said layer.

5. A screen for use with a television tube having a tube face, comprising the combination of an excitable phosphor layer precipitated on said tube face in the form of a substantially non-diffusing structure, and a second layer of light absorbent material, respecting light rays passing through said phosphor layer, near said phosphor layeron the opposite sidefrom that on which said tube face is located, so as to absorb light reflected from said phosphor layer.

6. In a screen for a television tube having a tube face, the combination of a fluorescent glassy layer on said tube face, and a coating of light absorbent material on the surface of said layer away from said tube face.

7. In a screen for a television tube having a tube face and electrodes for producing an electron beam for exciting said screen, the combination of a fluorescent layer on said tube face, and a coating of light absorbent material on said layer, said coating being of such thickness that the operation of said beam impinging on said layer is not impaired.

8. In a screen for a television tube having a tube face and electrodes for producing an electron beam for exciting said screen, the combination of a first layer of fluorescent material on the internal surface of said tube face, and a second layer of light absorbent material on the internal surface of said first layer away from said tube face, said second layer being of such a thickness that the operation of said electron beam respecting said first layer is not impaired.

9. The combination as claimed in claim 8 and in which said first layer is of a phosphor material, and said second layer is made of lampblack.

10. In combination, a cathode-ray tube having a tube face and means for directing an electron beam at said tube face, a fluorescent screen precipitated on the internal side of said tube face to form a transparent layer thereon, and a light absorbent layer, having a reflectance of less than 30% and of such thickness that the operation of said electron beam is not impaired. coated on said transparent layer on the opposite side thereof from said tube face.

11. In combination, a cathode ray tube having electrodes for producing an electron beam, and a screen disposed in the path of said beam, said screen comprising a transparent supporting material, a fluorescent layer precipitated on the internal side of said transparent material to form a transparent glassy layer thereon, and a coating of light absorbent material adjacent said fluorescent layer and of such thickness that the operation of said electron beam is not impaired, said coating being on the opposite side of said fluorescent layer from said supporting material.

12. A screen for a television tubing comprising: a transparent supporting layer, a fluorescent glassy layer on said supporting layer, and a coating of light absorbent material on said fluorescent layer.

13. A screen for a television tube comprising: a transparent supporting material, a fluorescent glassy layer on said material, and a coating of light absorbent material on the surface of said layer away from said supporting material.

JOHN W. COLTMAN.

REFERENCES CITED The following references are of record in the file of this patent:

UNITED STATES PATENTS Number Name Date 1,954,691 De Boer et al Apr. 10, 1934 1,982,373 Clinker et al Nov. 27, 1934 2,093,699 Varian et a1 Sept. 21, 1937 2,088,595 Hartmann Aug. 3, 1937 2,090,922 Von Ardenne Aug. 24, 1937 2,146,573 Hartmann Feb. 7, 1939 2,226,567 Le Van Dec. 31, 1940 2,312,206 Calbick Feb. 23, 1941 2,244,245 Ehrenberg June 3, 1941 2,233,786 Law Mar. 4, 1941 2,240,706 Law May 6, 1941 2,412,654 Sadowsky Dec. 17, 1946 2,446,248 Shrader Aug. 3, 1948 2,485,561 Burroughs Oct. 25, 1949 2,543,477 Sziklai Feb. 27, 1951 2,554,017 Dalton May 22, 1951 OTHER REFERENCES Pfund-Review of Scien. Instruments vol. I, July 1930 pgs. 397-399. 

1. IN COMBINATION: A CATHODE RAY TUBE HAVING A TUBE FACE AND ELECTRODES FOR PRODUCING AN ELECTRON BEAM; A FLUORESCENT LAYER PRECIPITATED ON THE INTERNAL SIDE OF SAID TUBE FACE TO FORM A TRANSPARENT GLASSY LAYER THEREON; AND A COATING OF LIGHT ABSORBENT MATERIAL, OF SUCH THICKNESS THAT THE OPERATION OF SAID ELECTRON BEAM IS NOT IMPAIRED, ADJACENT SAID FLUORESCENT LAYER ON THE OPPOSITE SIDE OF SAID FLUORESCENT LAYER FROM SAID TUBE FACE. 